Add tests for unavailability of `tee` and `splice` in `libc`
Add tests for unavailability of `tee` and `splice` in `libc`

As suggested by Paul Luse in review 135319 (for 2a0a8ae00f2), this
brings test coverage of the `swift.common.splice` module up to 100%.

The mechanism used to check whether the functions are looked up on `libc`
is somewhat ugly, but using a `PropertyMock` raising an `AttributeError`
as `side_effect` doesn't work: it results in `mock` creating a `Mock`
instance and returning it.

Change-Id: I14828cfc2ae644dbd9ead8c20613b19cea8607f1
See: https://review.openstack.org/#/c/135319/4/swift/common/splice.py,cm
See: 2a0a8ae00f2d3b7db255b0905b063e930f824f3d

bradleypj823/swift,maginatics/swift,dencaval/swift,rackerlabs/swift,mjzmjz/swift,Seagate/swift,larsbutler/swift,nadeemsyed/swift,bkolli/swift,matthewoliver/swift,matthewoliver/swift,bouncestorage/swift,takeshineshiro/swift,zackmdavis/swift,mjwtom/swift,mjwtom/swift,AfonsoFGarcia/swift,wenhuizhang/swift,bouncestorage/swift,notmyname/swift,clayg/swift,IPVL/swift-kilo,smerritt/swift,hbhdytf/mac2,dpgoetz/swift,eatbyte/Swift,notmyname/swift,thiagodasilva/swift,redhat-openstack/swift,williamthegrey/swift,bradleypj823/swift,maginatics/swift,zackmdavis/swift,prashanthpai/swift,hurricanerix/swift,iostackproject/IO-Bandwidth-Differentiation,clayg/swift,hbhdytf/mac2,swiftstack/swift,dpgoetz/swift,nadeemsyed/swift,eatbyte/Swift,aerwin3/swift,hbhdytf/mac,shibaniahegde/OpenStak_swift,revoer/keystone-8.0.0,IPVL/swift-kilo,Em-Pan/swift,matthewoliver/swift,bkolli/swift,anishnarang/gswift,smerritt/swift,shibaniahegde/OpenStak_swift,psachin/swift,hurricanerix/swift,hbhdytf/mac2,aerwin3/swift,tipabu/swift,swiftstack/swift,rackerlabs/swift,Em-Pan/swift,Seagate/swift,hbhdytf/mac2,notmyname/swift,openstack/swift,Akanoa/swift,redhat-openstack/swift,psachin/swift,hurricanerix/swift,daasbank/swift,hurricanerix/swift,nadeemsyed/swift,takeshineshiro/swift,clayg/swift,mjzmjz/swift,clayg/swift,gold3bear/swift,wenhuizhang/swift,tipabu/swift,notmyname/swift,psachin/swift,revoer/keystone-8.0.0,Akanoa/swift,dencaval/swift,matthewoliver/swift,williamthegrey/swift,smerritt/swift,gold3bear/swift,prashanthpai/swift,redbo/swift,daasbank/swift,levythu/swift,levythu/swift,psachin/swift,openstack/swift,hbhdytf/mac,nadeemsyed/swift,tipabu/swift,thiagodasilva/swift,redbo/swift,iostackproject/IO-Bandwidth-Differentiation,openstack/swift,tipabu/swift,openstack/swift,swiftstack/swift,smerritt/swift,larsbutler/swift,AfonsoFGarcia/swift,anishnarang/gswift